1. Field of the Invention
This invention relates to a temperature-compensated device for transmitting to a speed light a signal representing the exposure condition of a camera.
2. Description of the Prior Art
In recent years, the growth of electronic elements in flash photography devices comprising a combination of a camera and a speed light has advanced rapidly and various devices have been proposed in which an aperture value representing the exposure condition of the camera, a preset ASA value, etc. are also transmitted to the speed light to control the quantity of emitted light of a flash discharge tube in accordance with those values or to use those values to indicate a warning. Also, such speed light usually has a measuring operational circuit for effecting automatic light adjustment which is accurate to a certain degree. Now, the measuring operational circuit of this type, as is known in the camera art, includes a temperature coefficient in the transfer function (ratio of input signal to output signal) of the circuit and therefore, an input signal having a temperature coefficient reverse to said temperature coefficient is applied to such measuring operational circuit. By this, there is obtained an output signal having substantially no temperature coefficient. Thus, the input signal having a temperature coefficient corresponds to the previously mentioned aperture value or ASA value. Accordingly, in photography using only a camera, there is always obtained proper information by offsetting of such temperature coefficient. However, if an attempt is made to transmit to the speed light the information representing these exposure conditions as described above, a great problem occurs.
The problem is that the information having a temperature coefficient and representing the exposure conditions becomes information dependent on the temperature on the camera side and this becomes erroneous information in respect of the speed light which is at a different temperature. Thus, as hitherto described, in a single body such as the camera or the speed light, it is assumed that the ratio of the information applied to the aforementioned measuring operational circuit or other circuit to the finally produced information, namely, the overall transfer function as those single bodies, has no temperature-dependency.
So, for example, assume that, in a cold environment, a photographer who has so far carried out photography by using only a camera without using a speed light tries to effect flash photography by mounting to the camera the speed light which has so far been placed and warmed in his pocket or the like. The temperature difference between the camera and the speed light is great and therefore, the information transmitted from the camera to the speed light (in most cases, an electrical signal) has a temperature component different from that of other information produced by each circuit in the speed light. This has caused malfunctioning of the speed light (for example, a failure in the automatic light adjusting operation or in the warning indication that the setting was outside of the light adjustment range) which is essentially unavoidable.